The invention relates to a clamping device used in stretching metal sheets and plates. The clamping device is used in connection with a ductile metal sheet or plate straightening machine. The pulling heads of the clamping device are moved by a power drive. The pulling heads are equipped with a plurality of pairs of clamping jaws located across the width of the workpiece. The clamping jaws are guided by and slide over wedge-shaped, i.e., inclined surfaces of the pulling heads, and are slidable by the movement of hydraulic connecting rod-type devices between the projected out starting or initial clamping position and the retracted sheet metal release position.